Titanium dioxide dispersion

Abstract

To provide a titanium oxide dispersion that has high antifoamability, comprises reduced coarse particles, has excellent storage stability, does not cause oily film-like floats, and expresses excellent coating properties when used as ink raw material.SOLUTION: A titanium oxide dispersion comprises rutile titanium oxide (A), a dispersant (B), an antifoamer (C), and water. Relative to 100 pts.mass of the titanium oxide dispersion, the amount of the antifoamer (C) is 0.001-0.3 pt.mass.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a titanium dioxide dispersion. The titanium dioxide dispersion of the present invention can be particularly suitable for use as a raw material for inkjet inks. [Background technology]

[0002] Inks are broadly classified into two types: organic solvent-based inks, which use organic solvents as their main solvent component, and water-based inks, which use water as their main solvent component. Because organic solvent-based inks are less safe for human use and emit odors due to the organic solvents, water-based inks using aqueous solvents have been attracting attention in recent years. Furthermore, in recent years, inkjet recording devices, a digital printing method that does not require platemaking, have come into use to accommodate the printing of a wide variety of products in small batches. Rutile-type titanium dioxide, an inorganic pigment, is frequently used as a colorant in white inks for water-based inkjet printers. A method is employed in which a titanium dioxide dispersion (also called titanium dioxide paste or titanium dioxide slurry) containing a high concentration of rutile-type titanium dioxide is prepared, and this titanium dioxide dispersion is mixed with a water-soluble organic solvent, a resin dispersion, additives, water, etc., to produce white ink.

[0003] In water-based inkjet white inks, the low viscosity of the ink and the high specific gravity of rutile-type titanium dioxide make it prone to sedimentation, requiring redispersion processes such as circulation, shaking, and stirring during use. This process can easily generate bubbles, potentially negatively impacting the ink ejection head, thus requiring the ink itself to have high anti-bubbling properties. For example, Patent Document 1 shows that in an aqueous ink containing rutile-type titanium dioxide and a polymer dispersant, a high-acid value dispersant containing 72% by mass or more of components derived from anionic group-containing monomers can be used to obtain an aqueous white ink with excellent foam suppression properties that are less prone to foaming during redispersion.

[0004] For example, Patent Document 2 describes an aqueous white dispersion for inkjet inks comprising titanium dioxide particles with an oil absorption capacity of 25-50 g / 100 g, a dispersant, a basic compound, and water, wherein the titanium dioxide particles have a D10 average dispersion particle diameter of 120-220 nm and a D90 average dispersion particle diameter of 350-650 nm, and is an aqueous white dispersion for inkjet inks that has time-dependent dispersion stability that suppresses the sedimentation of pigment particles and can form a white ink layer with good whiteness. The example shows a titanium dioxide dispersion containing 1% by weight of Surfinol DF110D, an acetylene glycol-based defoamer, as an antifoamer in the titanium dioxide dispersion, and an aqueous white ink containing 1.25% by weight of the above-mentioned antifoamer made from the titanium dioxide dispersion as a raw material. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Patent No. 6881836 [Patent Document 2] Japanese Patent Publication No. 2021-105087 [Overview of the project] [Problems that the invention aims to solve]

[0006] Rutile titanium dioxide, used as a white pigment, has a high specific gravity and is prone to settling. Therefore, when using titanium dioxide dispersions as ink raw materials, a redispersion operation was necessary to homogenize the internal solid content concentration through shaking or stirring. However, the foaming properties caused by the dispersant, a surfactant, contained in the titanium dioxide dispersion made it difficult to sufficiently homogenize the internal solid content concentration during the redispersion operation. Furthermore, bubbles generated during the redispersion operation were entrained in the ink, causing problems when used as ink. Patent Document 1 concerns a type of dispersant with low foaming properties. It was difficult to obtain sufficient foam suppression in systems containing highly foaming dispersants such as those having polyoxyalkylene glycol groups, or in systems containing high concentrations of polymer emulsions with foaming emulsifiers.

[0007] The aqueous white ink in Patent Document 2 contains 1.25% by weight of Surfinol DF110D, an acetylene glycol-based defoaming agent, and thus has some degree of anti-foaming properties. However, it has the problem of causing oily film-like lifting due to the defoaming agent and adversely affecting the appearance of the coating film after printing. The object of the present invention is to provide a titanium dioxide dispersion that has high foam-suppressing properties, low levels of coarse particles, excellent storage stability, and exhibits excellent coating film properties and foam-suppressing properties when used as an ink raw material. [Means for solving the problem]

[0008] In view of the above-mentioned problems, the inventors conducted research and found that a titanium dioxide dispersion containing rutile-type titanium dioxide (A), a dispersant (B), an antifoaming agent (C), and water, wherein the amount of antifoaming agent (C) is 0.001 to 0.3 parts by mass per 100 parts by mass of the titanium dioxide dispersion, exhibits high antifoaming properties, has few coarse particles, excellent storage stability, does not produce an oily film-like surface, and exhibits excellent coating film properties and antifoaming properties when used as an ink raw material, thus completing the present invention. [Effects of the Invention]

[0009] The present invention provides a titanium dioxide dispersion that has high anti-foaming properties, low levels of coarse particles, excellent storage stability, no oily film-like floating, and exhibits excellent coating film properties and anti-foaming properties when used as an ink raw material. [Modes for carrying out the invention]

[0010] The titanium dioxide dispersion of the present invention is a titanium dioxide dispersion comprising rutile-type titanium dioxide (A), a dispersant (B), an antifoaming agent (C), and water, characterized in that the amount of antifoaming agent (C) is 0.001 to 0.3 parts by mass per 100 parts by mass of the titanium dioxide dispersion.

[0011] <Titanium dioxide dispersion> The titanium dioxide used in the titanium dioxide dispersion of this disclosure has three crystalline forms: anatase, rutile, and bluekite. From the viewpoint of opacity, it is preferable to use rutile titanium dioxide. The content of rutile-type titanium dioxide in 100 parts by mass of titanium dioxide of this disclosure is preferably 80 parts by mass or more, more preferably 90 parts by mass or more, even more preferably 95 parts by mass or more, and particularly preferably 100 parts by mass.

[0012] The primary particle size of titanium dioxide in this disclosure is preferably 0.1 μm or larger, more preferably 0.15 μm or larger, even more preferably 0.2 μm or larger, preferably 1 μm or smaller, even more preferably 0.4 μm or smaller, and even more preferably 0.3 μm or smaller. The primary particle size can be measured by scanning electron microscopy or transmission electron microscopy. The titanium oxide of this disclosure may be surface-treated. The surface treatment used may preferably include alumina (Al2O3), silica (SiO2), zirconium oxide (ZrO2), zinc oxide (ZnO), etc. From the viewpoint of wettability of titanium oxide and durability of printed materials when used as an ink, silica-alumina treated titanium oxide is preferred. The mass of silica and alumina present with titanium dioxide can be measured using X-ray fluorescence. Silica and alumina exist on the surface of titanium dioxide, and some may also exist as free particles. X-ray fluorescence measurement allows for the determination of their total amount. A quantitative analysis method using X-ray fluorescence has been established, employing a calibration curve with standard samples.

[0013] Examples of the rutile-type titanium oxide of the present disclosure include, for example, Typepe R-820, Typepe R-830, Typepe R-930, Typepe R-550, Typepe R-630, Typepe R-680, Typepe R-670, Typepe R-680, Typepe R-670, Typepe R-780, Typepe R-850, Typepe CR-50, Typepe CR-57, Typepe CR-Super70, Typepe CR-80, Typepe CR-90, Typepe CR-93, Typepe CR-95, Typepe CR-97, Typepe CR-60, Typepe CR-63, Typepe CR-67, Typepe CR-58, Typepe CR-85, Typepe UT771 (manufactured by Ishihara Sangyo Co., Ltd.), Typure R-100, Typure R-101, Typure R-102, Typure R-103, Typure R-104, Typure R-105, Typure R-108, Typure R-900, Typure R-902, Typure R-960, Typure R-706, Typure R-931 (manufactured by DuPont Kabushiki Kaisha), R-25, R-21, R-32, R-7E, R-5N, R-61N, R-62N, R-42, R-45M, R-44, R-49S, GTR-100, GTR-300, D-918, TCR-29, TCR-52, FTR-700 (manufactured by Sakai Chemical Industry Co., Ltd.), JR-403, JR-605, JR-806, JR-701, JR-805, JR-701, JR-800, JR-405, MT600B, MT150W (manufactured by Teika Corporation), etc. can be used. Etc. can be cited.

[0014] The titanium oxide dispersion of the present disclosure contains a dispersant (B) (hereinafter also referred to as a dispersant). The acid value of the dispersant (B) of the present disclosure is 5 mgKOH / g or more, may be 6 mgKOH / g or more, 7 mgKOH / g or more, may be 100 mgKOH / g or less, may be 80 mgKOH / g or less, but from the viewpoint of the dispersion stability of the titanium oxide dispersion, 60 mgKOH / g or less is preferable, 40 mgKOH / g or less is more preferable, and 20 mgKOH / g or less is even more preferable. As the dispersant (B) of the present disclosure, it preferably has a polyoxyalkylene glycol group, and a polyoxyalkylene glycol group-introduced acrylic dispersant is more preferable. Specific examples of the dispersant (B) of the present disclosure include, as commercially available products, Disperbyk-102, Disperbyk-111, Disperbyk-190, Disperbyk-191, Disperbyk-194N, Disperbyk-2010, Disperbyk-2012, Disperbyk-2015 manufactured by BYK Chemie Japan Co., Ltd., TEGO Dispers-715W, TEGO Dispers-750W, TEGO Dispers-755W manufactured by Evonik Japan Co., Ltd., Efka6230 manufactured by BASF Co., etc. Among them, Disperbyk-190, Disperbyk-191, Disperbyk-194N, Disperbyk-2010, Disperbyk-2015, and TEGO Dispers-750W are more preferable.

[0015] From the viewpoint of dispersion stability, the content ratio of the dispersant (B) to 100 parts by mass of titanium oxide of the present disclosure is 2% by mass or more, preferably 2.2% by mass or more, more preferably 2.5% by mass or more, further preferably 2.8% by mass or more. From the viewpoints of foam suppression property and physical properties of the coating film after ink formation, it is preferably 8% by mass or less, more preferably 7% by mass or less, and further preferably 5% by mass or less. If the content of titanium oxide in 100 parts by mass of the titanium oxide dispersion of the present disclosure is too low, the productivity will decrease, and when preparing an aqueous white ink using the titanium oxide dispersion as a raw material, it will be difficult to blend a sufficient water-dispersible resin as a binder, resulting in a decrease in various physical properties such as the scratch resistance of the coating film. If it is too high, the viscosity will increase and the dispersion treatment such as bead milling will be difficult. From these viewpoints, it is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, further preferably 40 parts by mass or more, preferably 70 parts by mass or less, more preferably 65 parts by mass or less, and further preferably 60 parts by mass or less.

[0016] The titanium oxide dispersion of the present disclosure contains an antifoaming agent (C) (hereinafter also referred to as an antifoaming agent). Defoaming agents are substances that eliminate or suppress foaming. Specifically, examples include silicone-based defoaming agents, polyether-based defoaming agents, fatty acid ester-based defoaming agents, and acetylene glycol-based defoaming agents. Among these, silicone-based and acetylene glycol-based defoaming agents are preferred because they have excellent ability to maintain surface tension and interfacial tension properly and hardly generate foam.

[0017] Examples of silicone-based defoamers in this disclosure include dimethylpolysiloxane, polyoxyalkylene-modified silicone, organically modified polysiloxane, and fluorosilicone. Commercially available examples include KS508, KS531, KM72, KM85 from Shin-Etsu Chemical Co., Ltd., Q-23183A, SH5510 from Toray Dow Corning, SAG30 from Nippon Unicar Co., Ltd., the Adekanate series from Asahi Denka Kogyo Co., Ltd., BYK-019, BYK-020, BYK-025, BYK-080A, BYK-094, BYK-1650, BYK-1660 from BIC Chemie Japan, and KF-6701 from Shin-Etsu Silicone Co., Ltd. Examples of polyether-based defoaming agents in this disclosure include the Adekapluronic® series and Adekanol® series (LG-109, LG-121, LG-294, LG-297, etc.) from Asahi Denka Kogyo Co., Ltd., and SN Deformer 157, 247, 375, 470, 777, etc. from Sunopco Co., Ltd.

[0018] Examples of fatty acid ester-based defoaming agents in this disclosure include isoamyl stearic acid, diglycol lauric acid, distearyl succinic acid, distearic acid, sorbitan monolauric acid, glycerin fatty acid esters, polyoxyethylene sorbitan, butyl stearate monolaurate, sucrose fatty acid esters, alkyl ethyl acetate esters of sulfonated lithinolic acid, and natural waxes.

[0019] The acetylene glycol-based defoaming agent of this disclosure may have the structure described in the following general formulas (1) to (6).

[0020] [ka]

[0021] [In formulas (1) to (3) above, R1 and R2 are alkyl groups having 1 to 8 carbon atoms, either linear or branched, and m, n, x, and y are numbers from 1 to 100.] Examples of acetylene glycol-based defoaming agents in this disclosure include acetylene glycol represented by formula (1) above, derivatives (adducts) of acetylene glycol represented by formula (2) above with ethylene oxide (EO) added, and derivatives (adducts) of acetylene glycol represented by formula (3) above with ethylene oxide (EO) and propylene oxide (PO) added.

[0022] Examples of linear or branched alkyl groups having 1 to 8 carbon atoms represented by R1 and R2 in formulas (1) to (3) above include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, t-butyl, pentyl, hexyl, heptyl, and octyl groups. Examples of the acetylene glycol of formula (1) above include 2,5,8,11-tetramethyl-6-dodecine-5,8-diol, 5,8-dimethyl-6-dodecine-5,8-diol, 2,4,7,9-tetramethyl-5-dodecine-4,7-diol, 8-hexadecin-7,10-diol, 7-tetradecine-6,9-diol, 2,3,6,7-tetramethyl-4-octin-3,6-diol, 3,6-diethyl-4-octin-3,6-diol, 2,5-dimethyl-3-hexyn-2,5-diol, etc. Examples of the alkylene oxide (EO, PO) adducts of the acetylene glycol of formulas (2) and (3) above include alkylene oxide derivatives of the above acetylene glycols.

[0023] The synthesis methods for each compound listed in formulas (1) to (3) above are known and can be obtained by various manufacturing methods, or commercially available products may be used. For example, examples of acetylene glycols and their alkylene oxide adducts include the commercially available Olphine series (manufactured by Nisshin Chemical Industry Co., Ltd.), Surfinol 104 [2,4,7,9-tetramethyl-5-dodecine-4,7-diol, manufactured by Nisshin Chemical Industry Co., Ltd.], Surfinol 104 series such as Surfinol 104E (ethylene glycol), 104H (ethylene glycol), 104A (2-ethylhexanol) obtained by diluting Surfinol 104 with various solvents, and 104S containing silica particles, as well as EO adducts of Surfinol 104 such as 420, 440, 465, 485, DF110D, DF37, DF58, DF75, and DF220.

[0024] Other defoaming agents that may be used include alcohol-based defoaming agents such as polyoxyalkylene glycol and its derivatives, polyoxyalkylene alcohol hydrate, diaminophenoxyethanol, 3-heptanol, and 2-ethylhexanol; ether-based defoaming agents such as 3-heptylcellosolve and nonylcellosolve-3-heptylcarbitol; phosphate ester-based defoaming agents such as tributyl phosphate, sodium octyl phosphate, and tris(butoxyethyl) phosphate; amine-based defoaming agents such as diamylamine; amide-based defoaming agents such as polyalkylene amide, acylate polyamine, and dioctadecanoylpiperidine; metal soap-based defoaming agents such as aluminum stearate, calcium stearate, potassium oleate, and calcium salts of wool olein; and sulfonate-based defoaming agents such as sodium lauryl sulfonate and sodium dodecyl sulfonate.

[0025] The content of the antifoaming agent (C) per 100 parts by mass of the titanium dioxide dispersion is preferably 0.001 parts by mass or more, more preferably 0.01 parts by mass or more, even more preferably 0.05 parts by mass or more, and from the viewpoint of suppressing the occurrence of floating on the oil film, it is preferably 0.5 parts by mass or less, more preferably 0.4 parts by mass or less, and even more preferably 0.3 parts by mass or less. The titanium dioxide dispersion of this disclosure contains water.

[0026] From the viewpoint of safety during titanium dioxide dispersion production, the water content in 100 parts by mass of the liquid phase component of the titanium dioxide dispersion of this disclosure is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The titanium dioxide dispersion of this disclosure may contain water-soluble organic solvents other than water. Ethylene glycol and propylene glycol are preferred as water-soluble organic solvents. From the viewpoint of safety during titanium dioxide dispersion production, the total content of water and water-soluble organic solvent in 100 parts by mass of the liquid phase component is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0027] Other additives that can be appropriately blended include plasticizers, leveling agents, fungicides, rust inhibitors, matting agents, flame retardants, thixotropes, tackifiers, thickeners, lubricants, antistatic agents, surfactants, reaction retarders, antioxidants, UV absorbers, hydrolysis inhibitors, weather stabilizers, and anti-tack agents. The blending ratio of each additive is appropriately selected depending on the purpose and application.

[0028] The amount of non-volatile components in the titanium oxide dispersion of this disclosure is preferably 20% by mass or more, more preferably 30% by mass or more, even more preferably 40% by mass or more, and particularly preferably 50% by mass or more, from the viewpoint of opacity and processing efficiency when used in printed materials. Furthermore, from the viewpoint of suppressing the viscosity of the titanium oxide dispersion, it is preferably 80% by mass or less, and more preferably 70% by mass or less. The non-volatile content of the titanium dioxide dispersion in this disclosure may be calculated as the total mass of the titanium dioxide dispersion minus the mass of water and volatile components contained in various additives, or by weighing 1 g of the titanium dioxide dispersion, drying it in a hot air dryer at a temperature of 150°C for 1 hour, and using the resulting residue as the non-volatile content, the formula is: [Non-volatile content (mass%) in titanium dioxide dispersion] = ([Mass of residue] ÷ [1g of titanium dioxide dispersion]) × 100 It may also be calculated based on this. If the viscosity of the titanium oxide dispersion of this disclosure is too high, dispersibility, bead separation when using a flow-type bead mill, and processing efficiency will decrease. If it is too low, the sedimentation rate of titanium oxide in the titanium oxide dispersion will increase, making it easier for hard cakes that cannot be redispersed to form. From these viewpoints, a viscosity of 1 to 200 mPa·s or less is preferred, more preferably 2 to 100 mPa·s or more, more preferably 5 to 50 mPa·s or more, and more preferably 10 to 20 mPa·s or more.

[0029] The viscosity of the titanium oxide dispersion of this disclosure at 25°C can be measured by known methods, specifically using a B-type viscometer or an E-type viscometer.

[0030] With respect to the titanium dioxide-containing particles (D) in the titanium dioxide dispersion of this disclosure, when the particle diameter of the cumulative 99% from the finest particle side of the volume-based cumulative particle size distribution is defined as the D99 particle diameter, the preferred upper limit of the D99 particle diameter is preferably 800 nm or less, more preferably 775 nm or less, and even more preferably 750 nm or less, from the viewpoint of the sedimentation stability of the titanium dioxide dispersion and the ejection stability when used as an inkjet-based white ink. The preferred lower limit of the D99 particle diameter is preferably 300 nm or more, more preferably 350 nm or more, and even more preferably 400 nm or more, from the viewpoint of preventing over-dispersion and thickening caused by the shedding of surface-treated metal oxides due to excessive bead milling.

[0031] With respect to the titanium dioxide-containing particles (D) in the titanium dioxide dispersion of this disclosure, when the particle diameter at which 50% of the cumulative particle size distribution from the finest particle side is taken as the D50 particle diameter, if the D50 particle diameter is too large, it will cause nozzle clogging when used as an inkjet ink raw material, and if it is too small, the opacity will decrease when used as an inkjet ink raw material. From these viewpoints, it is preferable that the D50 particle diameter be 500 nm or less, more preferably 450 nm or less, and even more preferably 380 nm or less. The lower limit of the average D50 particle diameter is preferably 150 nm or more, more preferably 200 nm or more, and even more preferably 250 nm or more.

[0032] The particle size in the titanium dioxide dispersion of this disclosure can be measured by known methods, specifically by dynamic scattering or Coulter counter methods.

[0033] Regarding the titanium dioxide-containing particles (D) in the titanium dioxide dispersion of this disclosure, if the particle concentration of particles with a diameter of 1.0 μm or larger is too high, it will cause nozzle clogging when used as an inkjet ink raw material, and if it is too small, the productivity of the titanium dioxide dispersion will decrease. From these perspectives, 1 × 10 6 ~200×10 6 It is preferable that the concentration is μm³ / ml, which is 3 × 10 6 ~100×10 6 μm 3 It is more preferable that it be / ml, which is 5 × 10 6 ~50×10 6 A concentration of μm³ / ml is even more preferable.

[0034] The concentration of particles with a diameter of 1.0 μm or larger in the titanium dioxide dispersion of this disclosure can be measured by known methods, specifically by the Coulter counter method or the like.

[0035] <Method for producing titanium dioxide dispersion> The titanium dioxide dispersion of this disclosure can be dispersed using known methods with titanium dioxide, a dispersant, an antifoaming agent, and water. By adding an antifoaming agent beforehand, it is possible to suppress a decrease in dispersion efficiency due to foaming, the occurrence of an oily film, an increase in D99 due to the antifoaming agent, and an increase in the concentration of particles larger than 1 μm. As for the dispersion method, a dispersion apparatus using media such as a ball mill, sand mill, or bead mill may be used, or a media-less dispersion apparatus may be used. In a dispersion device using media, zirconia beads are preferred as the dispersion medium from the viewpoint of dispersibility and dispersion efficiency. Furthermore, two or more of these dispersion methods may be used in combination. A dispersion apparatus using a bead mill is preferred as the dispersion method for the titanium oxide dispersion according to this disclosure.

[0036] The material of the bead mill is preferably a ceramic such as zirconia or titania, a polymer material such as polyethylene or nylon, or a metal, with zirconia being preferred from the viewpoint of wear resistance. For a bead mill, if the bead diameter is too small, the bead cost increases, and if it is too large, the processing efficiency decreases. From these viewpoints, a diameter of 0.01 mm or larger is preferred, 0.05 mm or larger is more preferred, 0.07 mm or larger is even more preferred, 1 mm or smaller is preferred, 0.5 mm or smaller is more preferred, and 0.2 mm or smaller is even more preferred.

[0037] The titanium oxide dispersion method of this disclosure may be a circulation method or a multi-pass method. A circulation method may involve installing a tank and a media-type disperser, forming a circulation system with piping, and circulating the dispersion. A multi-pass method may involve installing a mother tank, a receiving tank, and a media-type disperser, returning the dispersion from the receiving tank to the mother tank, or installing two tanks and a media-type disperser and passing the dispersion in a catch-and-throw manner. However, a circulation method is preferred from the viewpoint of simplicity of the equipment. Media-type dispersers may be installed in the required number of units arranged in series. The preferred circulation method of this disclosure is a circulation method in which a titanium dioxide dispersion containing titanium dioxide, a dispersant, and water is repeatedly circulated to a media disperser.

[0038] <Water-based white ink using titanium dioxide dispersion> If the amount of rutile-type titanium dioxide contained in the aqueous white ink using the titanium dioxide dispersion of this disclosure as a raw material is too low, the opacity decreases, and if it is too high, the ink viscosity increases and the printability decreases. From these viewpoints, the amount of rutile-type titanium dioxide contained in 100 parts by mass of aqueous white ink is preferably 1 to 25 parts by mass, more preferably 3 to 20 parts by mass, and even more preferably 6 to 12 parts by mass.

[0039] The aqueous white ink using the titanium dioxide dispersion of this disclosure contains a binder resin. In the aqueous white ink using the titanium dioxide dispersion of this disclosure as a raw material, the amount of binder resin relative to rutile-type titanium dioxide (mass of rutile-type titanium dioxide / mass of non-volatile content of the binder resin) is important. If it is too low, the opacity decreases; if it is too high, the abrasion resistance and gloss of the coating film decrease. From these viewpoints, a ratio of 2 / 10 to 6 / 1 is preferred, 5 / 10 to 2 / 1 is more preferred, and 6 / 10 to 1 / 1 is even more preferred.

[0040] The non-volatile content of the binder resin may be determined by referring to the value listed in the catalog, or by calculating it as the mass excluding the volatile components contained in the binder resin and various additives. Alternatively, 1 g of a water-dispersible resin containing the binder resin may be weighed, dried in a hot air dryer at 110°C for 1 hour, and the resulting residue may be used as the non-volatile content, using the formula: [Non-volatile content (mass%) in water-dispersible resins] = ([Mass of residue] ÷ [1g of water-dispersible resin]) × 100 It may also be calculated based on this.

[0041] The type of water-dispersible resin contained as a binder resin in the water-based white ink using the titanium dioxide dispersion of this disclosure as a raw material is not particularly limited, but from the viewpoint of improving the abrasion resistance of the coating film and adhesion to the substrate, acrylic resin, styrene-acrylic resin, and urethane resin are preferred. Among these, acrylic resin is preferred from the viewpoint of improving adhesion to poorly absorbent substrates such as plastics, and more preferably, from the viewpoint of obtaining good adhesion to poorly adhering olefin substrates such as biaxially oriented polypropylene (OPP) without primer printing, it is preferable that the water-dispersible resin contains a polymer having structural units derived from cyclic aliphatic group-containing monomers. The water-dispersible resin disclosed herein may be a single-layer resin emulsion particle or a resin emulsion particle having multiple layers.

[0042] The cyclic aliphatic group-containing monomers of this disclosure are preferably monomers having a carbon-carbon double bond, and include (meth)acrylate monomers having a cyclic aliphatic hydrocarbon group. The (meth)acrylate monomer having a cyclic aliphatic hydrocarbon group is preferably a compound having a monovalent cyclic aliphatic hydrocarbon group and a monovalent (meth)acrylate group, where the monovalent cyclic aliphatic hydrocarbon group and the monovalent (meth)acrylate group are directly bonded. Examples of cyclic aliphatic hydrocarbon groups include monocyclic groups, polycyclic groups, and cross-linked ring groups. The number of carbon atoms in the cyclic aliphatic hydrocarbon group is preferably 4 to 20. The cyclic aliphatic hydrocarbon group is preferably a cyclic aliphatic group having 4 to 20 carbon atoms, particularly 5 to 12 carbon atoms. The number of carbon atoms in the cyclic aliphatic hydrocarbon group is preferably 15 or less, for example, 10 or less. It is preferable that the carbon atoms in the ring of the cyclic aliphatic hydrocarbon group are directly bonded to the ester group in the (meth)acrylate group. Specific examples of cyclic aliphatic hydrocarbon groups are cyclohexyl group, t-butylcyclohexyl group, isobornyl group, dicyclopentanyl group, and dicyclopentenyl group. The (meth)acrylate group is either an acrylate group or a methacrylate group, but a methacrylate group is preferred.

[0043] Specific examples of monomers having a cyclic aliphatic hydrocarbon group include cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate, isobornyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentanyl (meth)acrylate, dicyclopentenyl (meth)acrylate, dicyclopentenyl (meth)acrylate, and dicyclopentenyl (meth)acrylate. Cyclopentyl (meth)acrylate, cyclohexyl (meth)acrylate, and isobornyl (meth)acrylate are preferred, and cyclohexyl (meth)acrylate and isobornyl (meth)acrylate are more preferred. These cyclic aliphatic group-containing monomers can be used individually or in combination of several types.

[0044] The content of structural units derived from monomers having cyclic aliphatic hydrocarbon groups in 100 parts by mass of the polymer having structural units derived from cyclic aliphatic group-containing monomers of the present disclosure may be 30 parts by mass or more, preferably 35 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 45 parts by mass or more, and may be 95 parts by mass or less, preferably 90 parts by mass or less, and more preferably 85 parts by mass or less.

[0045] When a water-dispersible resin containing a polymer having structural units derived from a cyclic aliphatic group-containing monomer is used as the binder resin of the present disclosure, the content of structural units derived from a monomer having a cyclic aliphatic hydrocarbon group in 100 parts by mass of the water-dispersible resin may be 30 parts by mass or more, preferably 35 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 45 parts by mass or more, may be 95 parts by mass or less, preferably 90 parts by mass or less, and more preferably 85 parts by mass or less.

[0046] The polymer having structural units derived from cyclic aliphatic group-containing monomers according to this disclosure may also have structural units derived from monomers other than those derived from cyclic aliphatic group-containing monomers. Other monomer-derived structural units are not limited to structural units formed by polymerization of the other monomers described below, but may also include structural units formed by post-reactions after polymerization, for example.

[0047] Other monomers include monofunctional monomers and polyfunctional monomers. Monofunctional monomers and polyfunctional monomers may be used individually or in combination. Examples of monofunctional monomers include (meth)acrylic acid esters having linear alkyl groups, (meth)acrylic acid esters having branched alkyl groups, acid group-containing monomers, hydroxyl group-containing (meth)acrylates, oxo group-containing monomers, fluorine atom-containing monomers, nitrogen atom-containing monomers, epoxy group-containing monomers, alkoxyalkyl (meth)acrylates, silane group-containing monomers, carbonyl group-containing monomers, aziridinyl group-containing monomers, styrene monomers, aralkyl (meth)acrylates, and addition polymerizable oxazolines, but are not limited to these examples.

[0048] The aqueous white ink disclosed herein may contain water or other water-soluble organic solvents from the viewpoint of controlling ink viscosity, wetting spread on the recording medium to be printed, improving image quality, and ejection stability. Examples of water-soluble organic solvents include glycols such as propylene glycol, 1,3-propanediol, glycerin, dipropylene glycol, tripropylene glycol, diethylene glycol, triethylene glycol, and tetraethylene glycol; monoethylene glycol ethers such as monoethylene glycol monomethyl ether, monoethylene glycol monoethyl ether, monoethylene glycol monopropyl ether, monoethylene glycol monoisopropyl ether, monoethylene glycol monobutyl ether, and monoethylene glycol monoisobutyl ether; monopropylene glycol monomethyl ether, monopropylene glycol monoethyl ether, monopropylene glycol monopropyl ether, monopropylene glycol monoisopropyl ether, and mono Monopropylene glycol ethers such as propylene glycol monobutyl ether and monopropylene glycol monoisobutyl ether; polyethylene glycol ethers such as polyethylene glycol monomethyl ether (moles of EO added = 2-10, preferably 2-4), polyethylene glycol monoethyl ether (moles of EO added = 2-10, preferably 2-4), polyethylene glycol monopropyl ether (moles of EO added = 2-10, preferably 2-4), polyethylene glycol monoisopropyl ether (moles of EO added = 2-10, preferably 2-4), polyethylene glycol monobutyl ether (moles of EO added = 2-10, preferably 2-4), and polyethylene glycol monoisobutyl ether (moles of EO added = 2-10, preferably 2-4);Examples of polypropylene glycol ethers include polypropylene glycol monomethyl ether (number of EO added moles = 2 to 10, preferably 2 to 4), polypropylene glycol monoethyl ether (number of EO added moles = 2 to 10, preferably 2 to 4), polypropylene glycol monopropyl ether (number of EO added moles = 2 to 10, preferably 2 to 4), polypropylene glycol monoisopropyl ether (number of EO added moles = 2 to 10, preferably 2 to 4), polypropylene glycol monobutyl ether (number of EO added moles = 2 to 10, preferably 2 to 4), and polypropylene glycol monoisobutyl ether. Among these, propylene glycol, diethylene glycol, triethylene glycol, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monoisopropyl ether, diethylene glycol monobutyl ether, diethylene glycol monoisobutyl ether, tripropylene glycol monomethyl ether, monoethylene glycol monoisopropyl ether, and monopropylene glycol monopropyl ether are preferred. These organic solvents may be used individually or in combination of two or more types. ;

[0049] The amount of water-soluble organic solvent varies depending on the type and amount of colorants contained in the water-based white ink, and therefore cannot be determined in general terms. It is preferable to determine the amount appropriately according to the type and amount of colorants contained in the water-based white ink.

[0050] For example, if the coloring agent contains a white pigment, the amount of organic solvent in 100g by mass of water-based white ink may be 5 parts by mass or more, preferably 8 parts by mass or more, more preferably 10 parts by mass or more, may be 50 parts by mass or less, preferably 45 parts by mass or less, and more preferably 40 parts by mass or less, from the viewpoint of controlling the wetting spread on the recording medium to be printed and improving image quality.

[0051] The aqueous white ink of this disclosure contains the aforementioned aqueous ink resin emulsion and colorant, but may also contain resins other than the aforementioned aqueous ink resin emulsion, water-soluble resins, water-dispersible resins, etc., as long as the objectives of the present invention are not hindered. Furthermore, the aqueous ink of the present invention may also contain appropriate amounts of additives such as surfactants, film-forming aids, ultraviolet absorbers, ultraviolet inhibitors, fillers, leveling agents, dispersants, thickeners, wetting agents, plasticizers, stabilizers, antioxidants, waxes, etc., as long as the objectives of the present invention are not hindered.

[0052] <Applications and substrates of the aqueous white ink using the titanium dioxide dispersion of this disclosure as a raw material> The aqueous white ink obtained as described above has excellent adhesion and scratch resistance, and can therefore be suitably used as an ink for various applications, such as water-based inkjet inks, flexographic printing inks, offset printing inks, lithograph printing inks, gravure printing inks, and screen printing inks, and is particularly suitable as a water-based inkjet ink.

[0053] The aqueous white ink of this disclosure can be used, for example, to form prints or images having a predetermined pattern by ejecting aqueous ink onto a recording medium in a predetermined pattern using an inkjet recording device, thereby obtaining printed materials using the aqueous ink of this disclosure. Examples of recording media include paper, paper laminated with resin films such as polyethylene, polypropylene, and polystyrene (such as coated paper), metal plates such as aluminum, zinc, and copper, resin films such as cellulose, polyethylene terephthalate, polystyrene, olefin resins, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyamide, nylon, and acrylic resins, paper with a metal coating, and resin films with a metal coating. Resin films are preferred as recording media for printing the aqueous ink of this disclosure, and among these, application to polyethylene terephthalate and olefin resins is preferred. Examples of olefin resins include polyethylene and polypropylene, with particular preference for application to polypropylene such as biaxially oriented polypropylene film (OPP) and unoriented polypropylene film (CPP).

[0054] The aqueous white ink of this disclosure is preferably formed on a resin film, and the embodiment thereof is a laminate having a printed layer formed from the aqueous ink on the resin film. The disclosed laminate may or may not have a primer layer between the resin film and the printed layer, but from a productivity standpoint it is preferable not to have one, and it is preferable to form the printed layer directly on the resin film. The disclosed laminate is laminated in the order of resin film and printed layer, and may or may not have a protective film (laminate layer) on the printed layer, but from a productivity standpoint it is preferable not to have one, and by using the aqueous ink of the disclosed, it is expected that a laminate with excellent adhesion to the substrate and good scratch resistance can be obtained even without a primer layer or protective film (laminate layer). [Examples]

[0055] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by mass" and "%" means "percent mass".

[0056] <Glass transition temperature of polymer components in water-dispersible resins> The glass transition temperature (Tg) of a polymer component is calculated using the glass transition temperature of the monomer homopolymer used in the monomer components constituting the polymer component, using the formula: 1 / Tg = Σ(Wm / Tgm) / 100 [In the formula, Wm represents the content (mass%) of monomer m in the monomer components constituting the polymer component, and Tgm represents the glass transition temperature (absolute temperature: K) of the monomer m homopolymer.] It was calculated based on Fox's formula, which is expressed as follows:

[0057] <Non-volatile content of water-dispersible resins> The non-volatile content was determined by weighing 1 g of water-based ink, drying it in a hot air dryer at 150°C for 1 hour, and considering the resulting residue as the non-volatile content, based on the following formula. [Non-volatile content (mass%) in water-dispersible resins] = ([Mass of residue] ÷ [1g of water-dispersible resin]) × 100 <Acid value derived from carboxyl groups of polymer components in water-dispersible resins> The acid value derived from the carboxyl groups of the resin emulsion particles was approximated by using the number of mg of potassium hydroxide required to neutralize the carboxyl groups present in 1 g of the monomer component used as the acid value.

[0058] <Minimum film-forming temperature for polymer components in water-dispersible resins> The minimum film formation temperature is measured in accordance with JIS K6828-2:2003, and the measured value is shown. <Average particle size of polymer components in water-dispersible resins> Using a multi-sample nanoparticle diameter measurement system [manufactured by Otsuka Electronics Co., Ltd., product name: nanoSAQLA], a particle size measurement device using dynamic light scattering at a measurement temperature of 25±0.5℃, the autocorrelation function was determined by photon correlation spectroscopy, and the average particle diameter (hydrodynamic diameter) was determined by cumulant analysis.

[0059] <D50 particle size, D99 particle size, and particle concentration of 1 μm or larger for titanium dioxide dispersion and aqueous white ink> The volume-based particle size was evaluated using the Multisizer 4e manufactured by Beckman Coulter, Inc. <Concentration of titanium dioxide dispersion> The concentration of the titanium dioxide dispersion was determined by weighing 1 g of aqueous ink, drying it in a hot air dryer at 150°C for 1 hour, and considering the resulting residue as non-volatile content, based on the following formula. [Non-volatile content (mass%) in titanium dioxide dispersion] = ([Mass of residue] ÷ [1g of titanium dioxide dispersion]) × 100

[0060] [Production example 1] Water-dispersible resin 520 parts of deionized water were placed in a flask equipped with a dropping funnel, stirrer, nitrogen gas inlet tube, thermometer, and reflux condenser. A first-stage dropwise pre-emulsion was prepared in the dropping funnel, consisting of 163 parts of deionized water, 80 parts of a 25% aqueous solution of emulsifier [ADEKA Corporation, product name: Adekaryasorb SR-10], 322 parts of cyclohexyl methacrylate, 103 parts of 2-ethylhexyl acrylate, and 75 parts of 2-hydroxyethyl methacrylate. 74 parts of this pre-emulsion, representing 5% of the total monomer components, were added to the flask. The temperature was raised to 70°C while slowly blowing in nitrogen gas, and 30 parts of a 5% aqueous solution of ammonium persulfate were added to initiate polymerization. Subsequently, the remaining portion of the dropwise pre-emulsion was uniformly added dropwise to the flask over a period of 120 minutes. After the dropwise dispensing was complete, the contents of the flask were maintained at 70°C for 60 minutes. Subsequently, a second-stage dropwise dispensing pre-emulsion consisting of 163 parts deionized water, 80 parts 25% aqueous solution of emulsifier [ADEKA Corporation, product name: Adeka Riasorb SR-10], 310 parts cyclohexyl methacrylate, 105 parts 2-ethylhexyl acrylate, 75 parts 2-hydroxyethyl methacrylate, and 10 parts 4-(meth)acryloyloxy-1,2,2,6,6-pentamethylpiperidine [ADEKA Corporation, product name: Adeka Stab LA-82], along with 30 parts 5% aqueous solution of ammonium persulfate, was uniformly added to the flask over 120 minutes.

[0061] After the dropwise addition was complete, the contents of the flask were maintained at 70°C for 60 minutes, and the pH was adjusted to 8 by adding 25% aqueous ammonia to complete the polymerization. After the resulting reaction solution was cooled to room temperature, a water-dispersible resin was prepared by filtering it through a 300-mesh wire mesh. The obtained water-dispersible resin contained a polymer, which was a resin emulsion consisting of two-layer emulsion particles with an inner and outer layer. The non-volatile content of this water-dispersible resin was 50%, the acid value derived from the carboxyl groups of the polymer was 0 mgKOH / g, the glass transition temperature of the inner layer resin constituting the resin emulsion particles contained in the emulsion was 32°C, and the glass transition temperature of the outer layer resin was also 32°C. The minimum film thickening temperature was 40°C, and the average particle size was 150 nm.

[0062] [Example 1] In a 250 mL plastic container, 40.87 parts of pure water, 4.13 parts of Disperbyk-190 (manufactured by Bic Chemie Japan, a polyalkylene glycol group-containing acrylic water-soluble resin, acid value 10 mg KOH / g, active ingredient concentration 40%) as a dispersant, 55.00 parts of JR-403 (manufactured by Teika, silica-alumina treated rutile titanium dioxide, primary particle size 250 nm) as rutile titanium dioxide, and 0.10 parts of Orfin D10-PG (manufactured by Nisshin Chemical Industry Co., Ltd., an acetylene-based surfactant) as an antifoaming agent were added. Subsequently, 100 g of 0.1 mm diameter zirconia beads were added as a dispersion medium. After sealing the plastic container and treating it with a paint shaker for 300 minutes, the zirconia beads were filtered by suction using a paper filter with a mesh size of 7 μm to obtain a titanium dioxide dispersion with a rutile titanium dioxide concentration of 55% by mass. Next, 24.5 parts of pure water, 15.0 parts of propylene glycol and 5.0 parts of tripropylene glycol monobutyl ether as water-soluble organic solvents, 20.0 parts of the above titanium dioxide dispersion, 35 parts of the water-dispersible resin obtained in Production Example 1 as a binder resin, and 0.5 parts of KF-6011 (manufactured by Shin-Etsu Chemical Co., Ltd.), PEG-11 methyl ether dimethicone (polyether-modified silicone surfactant) as a surfactant were mixed at 1000 rpm in a homodisper and filtered through a 3 μm filter [Advantec Co., Ltd., MCP-3-C10S] to obtain an aqueous white ink.

[0063] [Examples 2-4, Comparative Examples 1-5] Titanium dioxide dispersions and aqueous white inks were prepared using the same method as in Example 1, except that the type of defoaming agent was changed according to Table 1.

[0064] [Comparative Example 6] Titanium dioxide dispersions were prepared using the same method as in Example 1, except that the type of defoaming agent was changed according to Table 1. Subsequently, 24.5 parts of pure water, 15.0 parts of propylene glycol as a water-soluble organic solvent, 5.0 parts of tripropylene glycol monobutyl ether, 20.0 parts of the above titanium oxide dispersion, 35 parts of the water-dispersible resin obtained in Production Example 1 as a binder resin, 0.5 parts of KF-6011 (manufactured by Shin-Etsu Chemical Co., Ltd.) as a surfactant, and 0.02 parts of SN Deformer 777 (manufactured by San Nopco Ltd., silicone-based defoaming agent) were mixed with a homodisper at 1000 rpm and filtered through a 3 μm filter [manufactured by Advantec Co., Ltd., MCP-3-C10S] to obtain an aqueous white ink.

[0065]

Table 1

[0066] <Evaluation as a titanium oxide dispersion> Floating occurrence; There is no visually distinguishable oil film-like floating substance on the upper part of the liquid surface of the titanium oxide dispersion (A), a very small amount exists (B), and a large number exist (C). Defoaming property; When 50 g of the titanium oxide dispersion is placed in a 100 cc poly container and shaken well for 5 minutes, the bubbles generated disappear within 2 seconds (A), disappear within more than 2 seconds and within 5 seconds (B), and require more than 5 seconds to disappear (C). Particle concentration of 1 μm or more; 0 μm 3 / ml or more 25x10 6 μm 3 / ml or less (A), 25x10 6 μm 3 / ml exceeds 50x10 6 μm 3 / ml or less (B), 50x10 6 μm 3 / ml exceeds (C) <Evaluation as an aqueous ink> Defoaming property; When 50 g of the aqueous ink is placed in a 100 cc poly container and shaken well for 5 minutes, the bubbles generated disappear within 10 seconds (A), disappear within more than 10 seconds and within 30 seconds (B), and require more than 30 seconds to disappear (C). Coating film repellency; In a white coating obtained by coating a Futamura Chemical Co., Ltd. OPP film (FOR-AQ) with a #3 bar coater using water-based ink and drying at 110°C for 2 minutes, the number of circular repellencies visible per 500 cm² is less than 1 (A), 1 to 2 (B), or 3 or more (C). Table 2 shows the evaluation results for the titanium dioxide dispersions and aqueous inks of Examples 1-4 and Comparative Examples 1-6.

[0067] [Table 2]

[0068] In all examples containing the specified amount of defoaming agent, all items were rated B or higher, confirming that the properties were practically acceptable. In the comparative example that did not contain an antifoaming agent, both the titanium dioxide dispersion and the water-based ink received a C rating for foam suppression, indicating practical problems. In Comparative Examples 2-5, which contained 0.5 parts by mass or more of the defoaming agent, although sufficient anti-foaming properties were observed for practical use, it was found that lifting occurred in the titanium dioxide dispersion and coating film repellency occurred in the water-based ink, resulting in a C rating, which posed a practical problem. In Comparative Example 6, where a titanium dioxide dispersion without an antifoaming agent was used and a predetermined amount of antifoaming agent was added during the preparation of the aqueous ink, it was found that the concentration of particles larger than 1 μm derived from the antifoaming agent increased, posing a practical problem.

Claims

1. A titanium dioxide dispersion comprising rutile-type titanium dioxide (A), a dispersant (B), an antifoaming agent (C), and water, wherein the amount of antifoaming agent (C) is 0.001 to 0.3 parts by mass per 100 parts by mass of the titanium dioxide dispersion, the content of rutile-type titanium dioxide (A) is 20 to 70 parts by mass per 100 parts by mass of the titanium dioxide dispersion, and the antifoaming agent (C) is an acetylene glycol-based antifoaming agent or a silicone-based antifoaming agent, and is a titanium dioxide dispersion that serves as a raw material for inkjet ink.

2. The titanium dioxide dispersion according to claim 1, wherein the content of the dispersant (B) is 1 to 8 parts by mass per 100 parts by mass of rutile-type titanium dioxide (A).

3. The titanium dioxide dispersion according to claim 1 or 2, wherein the dispersant (B) is a polyoxyalkylene glycol group-introduced acrylic dispersant and has an acid value of 5 to 100 mg KOH / g.

4. A titanium dioxide dispersion according to any one of claims 1 to 3, wherein the D99 particle size of the titanium dioxide-containing particles (D) is 800 nm or less.

5. The titanium oxide dispersion according to claim 4, wherein the number of particles 1.0 μm or larger in the particle (D) is 200 x 10⁶ μm³ / ml or less.

6. An inkjet ink using the titanium dioxide dispersion described in any one of claims 1 to 5.

7. A printed material obtained using the ink described in claim 6.

8. A method for producing a titanium oxide dispersion according to any one of claims 1 to 5, which is prepared by bead milling with media with a diameter of 0.5 mm or less.

9. A method for producing a titanium dioxide dispersion comprising rutile-type titanium dioxide (A), a dispersant (B), an antifoaming agent (C), and water, wherein the amount of antifoaming agent (C) per 100 parts by mass of the titanium dioxide dispersion is 0.001 to 0.3 parts by mass, the content of rutile-type titanium dioxide (A) is 20 to 70 parts by mass per 100 parts by mass of the titanium dioxide dispersion, and the antifoaming agent (C) is an acetylene glycol-based antifoaming agent or a silicone-based antifoaming agent, the titanium dioxide dispersion is prepared by bead milling with media with a diameter of 0.5 mm or less.

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